Underboard-engined boats and propulsion means therefor



Dec. 14, 1965 J.J. HORAN 3,223,067

UNDERBOARD-ENGINED BOATS AND PROPULSION MEANS THEREFOR Filed Nov. 4, 1964 3 Sheets-Sheet 1 49 26 g. i? G if 4O 38 42 44 42 4| 37 43 45A /47 4| 50 J. J. HORAN Dec. 14, 1965 UNDERBOARD-ENGINED BOATS AND PROPULSION MEANS THEREFOR Filed Nov. 4, 1964 3 Sheets-Sheet 2 Fig, /0

J. J. HORAN Dec. 14, 1965 UNDERBOARD-ENGINED BOATS AND PROPULSION MEANS THEREFOR Filed NOV. 4. 1964 3 Sheets-Sheet 5 United States Patent 3,223,067 UNDERBQARD-ENGINED BOATS AND PROPUL- SIGN MEANS THEREFOR John J. Horan, 420 Quigley Ava, Willow Grove, Pa. Fiied Nov. 4, 1964, Ser. No. 409,(i20 25 Claims. (Cl. 11535) This invention relates to a distinctive new form of Watercraft and to the unique propulsion arrangements therefor. This application is filed as a continuation-in-part of my copending applications entitled: Watercraft and Propulsion Means Therefor, Serial No. 248,426, now US. Patent No. 3,161,173, and Propulsion Means for Watercraft, Serial No. 337,120, now US. Patent N0. 3,162,481, which represents a division of the first-named.

Like the co-pending applications, this one teaches the underboard engine-watercraft relationship, as distinct from the inboard and out outboard types of the prior art. By underboard is meant the placement of the main portion of the engine beneath the hull instead of perching it upon the hull, on brackets or mounts within the hull, or upon the transom.

This application teaches that the installation, servicing, and removal of underboard engines can actually be accomplished safely, conveniently, expeditiously, and easily by one person, without tools, from a position within the boat itself; and it teaches that these operations can be performed also on engines that are fully capable of steering the craft and reversing it without stopping the motor, shifting gears, or using a clutch. In fact, the underboard engine can afford the lowest-cost installation and the handiest and simplest possible motive power for small boats.

To keep this application from becoming too lengthy, I have confined the illustrations to a single type of onecylinder engine; but it will be obvious that there are no inherent limitations either as to the size or number of cylinders in the power plant or as to the size of the boat in which an underboard engine may be installed. When larger engines are dropped through the hulls of larger craft, the same general principles of mounting and installation will still apply. Steering is handily accomplished by a forward-facing operator who does not have to perch forward of a low transom, twist his body around to operate the engine, and peer around a soaring bow to see where he is going; nor must complex and expensive control systems be installed to permit the operator to sit elsewhere.

The shortcomings of inboard-engine boats, as compared with boats equipped with outboard engines, and vice versa, have been so abundantly and redundantly described by the advocates and critics of the two old camps that there is no need for repeating the deficiencies here. Unlike the older types, the wet-skinned underboard engines of this application weigh less than comparable engines of either old family; and they do not grievously unbalance the boat with a heavy load aft. They can be placed where their weight and their propeller can do the most good. They have the lowest center of gravity ever achieved in marine craft; and, in fact, they contribute a positive stabilizing moment unique in the history of motorboating instead of reducing the stability of the boat as do both of the prior classes. They impose no limitation on the height of the transom that might impair the safety of the boat in a following sea; they do not impose the burden of a huge engine installation clogging the center of the cockpit; they have no shaft tunnel and no troubles with inaccessible tunnel packing glands; they need no cooling pumps, nor heavily finned, complex and costly air cooled castings, nor costly water-jacket corings with all the leaks with which the joints between such castings are likely to suffer.

Displacement for displacement, or power for power,

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the underboard engine is invariably simpler and smaller; and it takes up less of the otherwise useful passenger room for its accommodation and weighs less than either of its predecessors.

An object of this invention is to teach the design of boats that will permit engines to be installed under their hulls and be removed therefrom conveniently after each trip or each days use, if desired, safely and handily, without tools, from a position Within the boat while it is on the water, by a single person.

An object of this invention is to carry on with the teaching of design principles for engines that will permit them to function properly while immersed in water under a boat.

An object of this invention is to each the principles. of steering a boat with an underboard engine.

An object of this invention is to teach the principles of mounting and adaptation of internal-combustion engines so as to permit them to be serviced, started, and operated safely and conveniently under the hulls of boats by a forward-facing occupant seated comfortably within the passenger compartment.

An object of this invention is to show that an underboard engine can be sufficiently cowled or otherwise streamlined to minimize its water drag under the hull of a boat.

An object of this invention is to develop a new marine art for the purpose of reducing the complexity and cost that were inherent in the inboard and outboard power plant systems of the prior art.

Other objects and novel features are contained in the claims, the specification, and the appended drawings, in which:

FIG. 1 is a partly sectioned side elevation showing an engine similar in size and style to that portrayed in FIG. 10 of each of the prior patent applications above-mew tioned, together with its underboard mounting arrangement adapted for use with a small boat, in accordance with this invention;

FIG. 2 is a front elevation showing the relationship of the cowling of the engine of FIG. 1 to the undersurface of the boat hull of FIG. 1;

FIG. 3 is a view looking down into the cowling of FIG. 1, with the engine removed;

FIG. 4 is a sketch showing how the retaining cover of FIG. 1 may be applied to supporting the engine temporarily in a raised position;

FIG. 5 is a side elevation of a second mounting arrangement using substantially the same engine employed in the prior embodiment;

FIG. 6 is a front elevation of the underboard cowling for the engine of FIG. 5;

FIG. 7 is a view looking down upon the mounted engine of FIG. 5;

FIG. 8 is a partly sectioned elevation of a third underboard mounting arrangement having an engine similar to that of FIG. 1;

FIG. 9 is a view from above the mounting arrangement for the engine of FIG. 8, with the cover removed;

FIG. 10 is a view of a fourth mounting arrangement showing a modified engine having the general character of that shown in FIG. 1.

In connection with the above-designated figures, my selection of a group of generally similar engines for the illustrations herein was made for the purpose of simplifying the presentation and making easy the task of understanding its purpose and content. A variety of engine configurations might well have been selected, with a View toward detailing all-inclusively the scope of engine configurations to which the principles of this application can be applied. Alternatively each engine might have been extensively reconfigured for maximum suitability for coaction with the mounting arrangement with which it is portrayed. However, this invention is concerned less with the actual engine design than it is with the broad purpose of adapting such engines and boat forms generally to complement each other in the novel underboard relationship and function, which adaptation, into a complementing relationship, constitutes the kernel of this invention.

Referring now to FIGS. 1 through 4, there is shown an internal-combustion engine 21 adapted to function in water. The engine 21 has an unusually slim contour, its configuration resulting from a number of novel features previously described in connection with FIG. and other figures contained in the above-mentioned co-pending applications. The combustion Zone of internal-combustion engine 21 is within immersion-cooled cylinder 22, which is its exterior wall. The single cylinder 22 of the engine 21 is aligned so that its axis coincides generally with the path traveled by the engine as it advances through the water. The spark plug is housed in the sealed can 23 at one end of the cylinder. The carburetor 24 stands above the crankcase 25; and the muffler 26 rises above the cylinder 22 as an air trap, the exhaust pipe 27 dropping away from the muffler 26 and terminating 28 aft of the engine just outside the arc of the propeller 33, which is mounted on the submerged shaft issuing from the crankcase end of engine 21.

Magneto 29 has been relocated from its position in the prior applications as a result of eliminating the engineswiveling feature seen in FIGS. 10, 18, and 19 of the prior applications and switching the magnets from one crankwheel to the other.

Although the absence of valves and carburetion from the head end of the cylinder 22 marks the illustrated engine as being of the two-stroke-cycle type, and although the general preference in small marine engines is for 2-cycle gasoline-driven types because of their light weight, high r.p.m.-capability, and mechanical simplicity, it will be appreciated that the carburetors, manifolds, etc., for other spark-ignition engines can project upwardly in the same manner as shown for exhaust passages and combustion intakes in the figures and that breathing, fuel injection, etc., for diesel engines likewise impose no unique, unsolved problems not taught by reference to this application plus the prior art. Valve-gear covers, etc., can be sealed by conventional methods against leakage while in the enveloping coolant bath.

Cowlings are not categorically essential as such to all underboard engines; but this particular cowling 31, of thinwalled contoured sheet material, has another function besides complementing cover or guard 43 in forming a compartment for cooling regulation and the streamlining of the power plant, that of serving as a bridging structure for supporting the engine and delivering the thrust of the engine 21 to the boat via its flange 37 and the rim or mounting ledge 40 bordering the opening in the boat hull. Vent 32 admits water for cooling and valve 34 regulates the outflow. The mounting arrangement includes clamping rings 35 and 36 on the engine 21, attached by screws to the cowling 31. The aft end of cowling upper flange 37 has a pivoting portion 38 that seats in a mating groove 39 at the aft end of rim 40. The ridge 41, 41, which is part of rim 40, keeps the cowling 31 from trying to shift position as it delivers the thrust of the engine. Gasket 42, 42 surrounds this ridge, providing a sealing seat for guard 43, which keeps the engine 21 and cowling 31 from moving upward out of position when carrying thrust.

Guard 43 pivots on pin 44 which is set on blocks 45 on the bottom of the hull. When raised, as in FIG. 4, guard 43 provides a seat for temporarily propping or resting the non-pivoting end of cowling 31. The water drains through valve 34, enabling the occupant to service the engine .21 out of water. In this position, the occupant, by pulling on starter handle 46, can start the engine most readily because it is not under load; and he then may drop the cowling 31 and engine 21 down and re-close the guard 43.

The manifold 47 lies between the carburetor 24 and the crankcase of the engine 21. The manifold 47 carries externally a gasket 48 which seals around the periphery of the airduct opening 43A in guard or cover 43, which cooperates with the carburetor in providing a sealed, gasketed 48, air-breathing duct leading downward from within the hull 51 into engine 21. Theopening allows the guard to clear the carburetor 24 as it swings down and closes. The guard 43 has a domed portion 49, which gives clearance for and aflords the occupants burn protection from the mufiler 26. The guard 43, when in the raised position for engine starting, is made more secure by pin 52, a locking member for cowling or bridging structure 31, which fits in vent hole 32 of the cowling. While the engine is running, the guard 43 is clamped down by swiveling dog 50, which, together with ledge or rim 40, ridge 41, pivot pin 44, gasket 42, and guard or cover 43, constitutes a clamping array for holding bridging structure or cowling 31 and engine 21 down finnly in place. When upward exhaust is acceptable, a pipe such as 53 (dashed lines) may be routed as shown. Alternatively, the dome 49, the muflier 26, and the terminal portion 28 of the exhaust pipe might all have been omitted altogether.

The engine-mounting arrangement described in connection with FIGS. 1 through 4 is particularly applicable to a small twin-catamaran-hulled boat (or pontoonhulled) with the deep-hulled portions so close together as not to allow the engine to swivel. Auxiliary rudder means would be needed. In this instance, the boat would be designed so that the presence of an occupant would depress the pontoons or catamaran portions until the level of the hull at the engine location approaches the water surface.

It will be seen that this mounting arrangement permits an occupant, working wholly inside the boat, and not forced to lean over a shallow transom, to install conveniently, remove, service, or start an underboard engine, and to perform all these operations, except servicing, without Referring now to FIGS. 5, 6, and 7, there is shown the same basic engine with an underboard mounting arrangement of different character that carries certain advantages. In the prior construction, the cowling 31 was seated by its flange in the bottom of the hull, thus serving as part of the engine mounting. This time, the cowling has an inwardly turned flange 61 which does not rest on the hull bottom 62, but, instead, drops cleanly through the rim 63 of the opening in the hull. Propeller 33, vent 32, and valve 34 have functions and relationships to engine 66 similar to those previously described for propeller -33, vent 32, and valve 34, used with engine 21 in FIGS. 1 through 4.

A generally cylindrical adapter casting or circular bridging structure 64 supports engine 66 across the openmg and makes it possible to rotate about a vertical axis as a single unit this structure and the elongated engine, propeller and cowling assembly, together with all included ductwork for air and waste gases. The bridging structure 64 rotates upon the circularly arrayed guide surfaces constituted by the cutting of shelves or ledge means 72, 73 into rim 63 of the hull opening. The bridging structure 64, having an integral circular flange or rim portion 65, is secured by screws to the crankcase of the engine 66 via its inwardly turned bottom flange 67. Engine 66 drives propeller 33. The D-shaped chamber of this bridging structure 64, seen best in FIG. 7, constitutes a duct, gasket-sealed 77 to the opening 76A in cover 76 against counterflow of water, for the passage of air into the engine 66; and it permits a carburetor to be dropped thereinto above the row of reed-valve-equipped inlet ports 68 in the crankcase. The fuel tank 74, not shown in FIG. 7, may be inverted and inserted above the carburetor. Fuel tank 74 has a base 75, adapted to serve as a steering wheel, and a hollow central tube 176, through which the engine receives its air supply. Sealing means, located, at choice, under the gas tank, beneath the carburetor, or around the carburetor, is required, of course, in order that uncontrolled amounts of air will not bypass the carburetor.

Opposite the D-shaped chamber housing the carburetor is a smaller D-sha-ped chamber having a lateral opening under and radially within rim portion 65 of bridging structure 64, aifording upward clearance from below on the far side, as viewed in FIG. 5, into which the intermediate bent-up portions 69 of the exhaust pipe or waste-gas duct 70, 71 are led to provide an inverted trap against flooding bent-over and 70, 71 are led to provide an inverted trap against flooding of the engine via the exhaust pipe 70, 71 by the coolant. This latter chamber is closed off at the top, as may be observed in FIG. 7, alfording a sealed barrier against any surge of water from below.

The diameter of the flange, or rim portion, 65 of the bridging structure 64 is too great to permit it to be admitted past the rim 63, which has already admitted the cowling 60; so the flange 65, or circularly contoured rim of demountable bridging structure 64 rests on the flanking shelves 72, 73, or mounting ledge portions of the circularly arrayed guide surfaces, that remain when clearance for the flange 65 is cut into the upper surface of the rim 63. The flange or rim portion 65, therefore, rotates freely about a vertical axis on the flanking shelves or circularly arrayed mounting ledge 72, 73, when the Wheel 75 is rotated by the occupant to steer the boat. Sealing against water entry into the boat is afforded by hold-down plate or cover means 76, which has a sealing undersurface 77 consisting of a thin layer of closed-cell foam rubber. Cowling 60, undersurface 77 of cover 76, and rim 63, including ledge means 72, 73, form a compartment which inhibits water circulation around engine 66, keeping it from being overcooled. Plate 76 is held down against lifting forces by a set of swing-away dogs 78, which dogs, plus the cover plate and its undersurface 77, are a clamping array that confines bridging structure 64 on ledges 72, 73 and positions engine 66 to hold its combustion zone under water, as in the previous engine. Since complete closure of the bottom opening is preferred when the boat is moored without its engine, a small cover plate, not shown, may be used to span the opening provided in hold down plate 76. Cover plate 76 has an opening 76A, providing clearance for the adapter casting, which, among other functions, contains the intake passageway for combustion air.

Although the cowled engine, together with propeller 33, constitutes a longer assembly than the hull opening, it is easily lifted out by tilting the forward end upward.

The engine 66 may be rotated as much as necessary to turn or even to reverse the boat without stopping the engine and without resorting to reversing gears or to means for changing the direction of run of the engine. Like the prior engine, it is preferably located between flanking catamaran or pontoin-type downward hull projections that cause the water, when the boat is occupied prior to installing the engine, to approach but not to exceed the level of the bottom 62. By reversing engine rotation, the installation is changed to tractor type.

Referring now to FIGS. 8 and 9, there is shown a third embodiment of the underboard engine installation, incorporating the same basic engine seen in the prior figures. The engine 91 and cowling 92 are secured, fore and aft, to the dishpan-shaped tub 93, which constitutes a demountable, rotating, bridging structure spanning the hull opening upon the rim or ledge means 97, which means affords a circularly arrayed guide surface for the matching rim of tub or bridging structure 93. Structure 93, carries an upwardly extending wall formation constituting a dry compartment above engine 91, and which, together with ducts, etc., therewithin and items carried thereon, rotates about a vertical axis, carrying engine 91 and propeller 33. Tub or bridging structure 93 is adapted to be rotated in place for steering or reversal by the transverse bar, which comprises a rod 94 and a receiver member 95 containing a compression spring within the large-diameter portion 96. The transverse bar seats at opposite ends in holes drilled in the tub 93. The tub 93 rides for rotation on the rim 97 of the opening in the boat bottom 98. The rim 97 and the upwardly projecting wall formation 99 extend nearly all the way around the opening in the bottom, becoming discontinuous as they intersect the sidewalls 100, 101 of the raised ramp portion 102 aft. Thus the tub 93, and the engine with it, may be rotated through multiples of 360 if desired. Since the wall 99 and the ramp sidewalls 100, 101 give 360 protection up to their full height against entry of water upward into the boat, it is unnecessary to provide gasketing between the tub 93 and any part of the bottom 98; so the boat may be operated with the tub 93 remaining open at the top and the cover 103 removed or open, provided that spring-biased latch pins 104 are secured. A further advantage of this embodiment, as well as the prior one, is that it permits the opening in the boat bottom to be shorter than the overall length of the engine and propeller. The primary difference here is in the additional hull-closure means constituted by the sloping ramp, which decreases only the effective area of the opening at the upper level, whereas the actual opening goes well aft between the sidewalls of the elevated ramp structure, permitting the engine to be elevated for starting.

The engine 91 may be started without load, as long as the cover 103 is open, by lifting the tub 93 by the transverse bar 94, 95 a suflicient height to permit latch pins 104 to slip under the edge of the tub 93 and hold the entire tub and engine assembly in a raised position, as a temporary mounting ledge therefor. The T-handle 105 is removed from its clip inserted via the opening 107, and screwed into the fitting 108 on the end of the starter rope 109, thus aifording a convenient extension for the starter rope 109. The whole assembly is then lowered after starting to operating position when pins 104 are withdrawn temporarily. They automatically re-latch the engine 91 in the down position when they re-engage the tub 93. In this case, cowling 92 may be attached for convenience either to the engine 91 or to the tub 93, since the cowling 92 performs no structural function. If the engine is made smoother in external configuration than the one shown, and if adequate means are adopted to prevent over-cooling the cowling may be eliminated.

Arrayed in the tub 93 above the engine 91, are the mufller 110, which projects as an anti-flooding ducted gas-trap loop upwardly via a clearance opening in tub 93 into the interior of the guard or upwardly recessed closure 111, which is an inverted cup secured at its flange 112 by screws 113 to the tub floor. Also in the tub are the fuel tank 114, and the carburetor 115, which includes a small plenum or manifold, not visible, at its base where it is ducted into the engine through the bottom of tub or bridging structure 93 over the reed ports in the crankcase, the air inlet 116, and a fuel line 117. The necessary engine-breathing opening through the bottom of tub 93 between carburetor means 115 and engine 91 does not show in the figures because it is located directly under carburetor means 115 in FIG. 9. It'has the same general purposes and functions as prior-described openings 43A and 76A, that is, to allow sealed clearance for the engine air-intake ductway.

When the engine and tub assembly are removed, cover 103 may again be closed as shown. It would normally be closed only when the engine is not operating, because of the need for steering access. Cover 103 maybe made of flexible material if preferred. Also, if preferred, a steering means may project upwardly through an opening centrally located over the tub 93 in the cover 103. In some instances, it will be found that greater speed may be obtained when opening 107 is left open than if it is plugged. It may be desirable to have an even larger opening area, proportionately, than that existing in opening 107 for the entry of suflicient aspirated air under the hull at higher speeds.

Referring now to FIG. 10, there is seen a basically similar engine 120, with certain changes, including the enclosure of the magneto coil and the changing of the diameter of the propeller 134 (for which one might modify bore, stroke, or bevel-gear ratio or change to other form of gearing). The rotatable and demountable tub or circular bridging structure 121, upon which is borne the propulsion-system assembly, including engine 120, also carries certain ancillary items within its raised circular wall formation that describes a compartment above the engine 120, but it is quite different from the prior one; and it encloses substantially the upper half of the engine 120, leaving the greater burden of cooling now on the lower portion of the engine which now has no cowling.

Instead of the rigid wall and ramp arrangement in the prior embodiment, there is an upwardly projecting, collapsible, curtain-type wall formation 122, made of flexible, waterproof sheet material, mounted on the ledge inboard of the opening in hull bottom 124 and in turn surmounted by a second ledge or mounting flange 123 and propped or biased upwardly by a spring means, such as 125, so as to bar water entry over the top of elevated flange or mounting ledge means 123, when the engine or cover is not present. The combined weight of engine 120, tub 121, cover 126, etc., partly counterbalances the spring force; and suflicient hooks 127 are provided to lash the whole assembly in the down position when the engine is running. Closed-cell-foam gasket 128 bars entry of water into the boat when dogs 135 are moved radially inward into hold-down position. These dogs 135, together with hooks 127, cover 126, gasket 128, and mounting-ledge means 123, constitute the clamping array which projects and secures the propulsion-system assembly down, exposing the lower wall of the combustion zone of engine 120 to the coolant water under the hull 124. Under cover 126 are seen dotted outlines of muffler 129, carburetor 130, and gas tank 131, the breathing air entering the engine via the carburetor 130 and an opening in the tub 121, therebelow, which is hidden from view by other details in FIG. 10. The plug 132 is removed to admit air when the engine is to run. Replacing it would quickly stifle any gasoline fire. Dotted outline 133 indicates a plug that is removed before starting the engine. Starting would normally be done with the cover 126 removed and the engine and tub assembly elevated to take the load propeller 134. Fingers 138 or oher alignment devices may be used to restrict lateral movement during starting. Handle 136 is used for steering. Alignment between cover 126 and tub 121 (and, therefore, the engine) is assured by dowel 137, which is seen in FIG. 10 to key the circular rim portions of cover 126 and tub or bridging structure 121, and thereby engine 120, to steering control about a vertical axis, by above-mentioned handle 136, upon stationary ledge means 123, in a manner similar to the control that was seen exerted in the prior species by trans- .verse bar 94, 95 on tub or bridging structure 93 and engine 91. Height variability in wall 122 may be achieved by means other than the use of flexible material in its structure. Other means, for example, of achieving a like end include use of segmented or of nested components.

It will be obvious that various combinations can be made of inventive features I have shown. Such combinations will become immediately obvious to those skilled in the art, without departing from the true scope of this invention. It is most obvious that major improvements over the old art can be accomplished by the adoption of only portions of the inventive features disclosed hereinabove. New equivalents of the embodiments introduced and taught here will immediately suggest themselves. It is, accordingly, intended to include in the appended claims such portions and equivalents as may fall Within the true scope of my invention. I wish it understood that my invention is not to be limited to the specific forms or arrangements to which I have limited my descriptions, drawings, and claims for the sake of brevity and expeditious prosecution.

I claim:

1. A watercraft having a hull with a downward opening through the bottom thereof;

an upwardly projecting wall formation supported on said hull and bordering said opening,

said wall formation having an upper portion,

said upper portion having ledge means thereon,

said ledge means being adapted to receive thereon a demountable propulsion-system assembly,

said portion being adjustable as to height of rise thereof within said hull;

and a spring device biased to displace said portion upwardly.

2. A watercraft having a hull with a downward opening through the bottom thereof;

an upwardly projecting wall formation supported on said hull and bordering said opening;

a mounting ledge means surmounting at least a portion of said wall formation and adapted to receive thereon a demountable propulsion-system assembly,

said wall formation being adjustable as to height of rise of said ledge means within said hull,

said wall formation being attached to said hull and consisting at least in part of flexible material intervening between said hull and said ledge means.

3. A watercraft as in claim 2,

said watercraft including also guidance means projecting upwardly of said bottom and situated in way of excessive horizontal motion of said wall formation.

4. A watercraft having: a hull with a downward opening through the bottom thereof,

said hull having a mounting ledge means bordering and defining at least a portion of said opening,

said means being adapted to receive thereon a demountable propulsion-system assembly comprising:

a bridging structure adapted to seat on said ledge means and extend across said opening;

an internal-combustion engine depending at least in part below said bridging structure,

said structure having a smaller opening therethrough for passage of air from within said hull downwardly into said engine;

retaining means for holding said structure down on said ledge means against lifting forces;

and propeller means mounted on a rotating shaft projecting from and driven by said engine,

a portion of said opening through the bottom of said hull extending beyond the limits of said bridging structure,

said bridging structure and said ledge means having matching, generally circularly arrayed mating surfaces,

whereby said bridging structure and engine may be rotated for steering said watercraft.

5. A watercraft having a hull with a downward opening through the bottom thereof,

said hull having a mounting-ledge means bordering at least a portion of said opening,

said means being adapted to receive thereon a demountable propulsion-system assembly comprising:

a bridging structure adapted to seat on said ledge means and extend across said opening;

an internal-combustion engine depending at least in part below said bridging structure,

said structure having a smaller opening therethrough for passage of air from within said hull downwardly into said engine;

retaining means for holding said structure down on said ledge means against lifting forces;

and propeller means mounted on a rotating shaft projecting from and driven by said engine, said bridging structure having a generally circularly arrayed contour where it seats on said ledge means and having a central generally vertical axis of rotation, said hull having a circularly arrayed guide surface on said ledge means to match said contour, said bridging structure being free to be rotated in place about said axis upon said ledge means, whereby said propulsion system may be rotated in place and said watercraft may be steered. 6. The combination of claim 5, said bridging structure having a cavity contained within the diameter of said circular contour and opening upwardly into said structure from below; and exhaust-pipe means extending from said engine and discharging into the water under said watercraft, said exhaust-pipe means having therein an upwardly directed loop portion forming a gas trap against influx of water into said engine via said exhaust pipe, said loop portion entering upwardly into said cavity in said structure. 7. A watercraft comprising: a hull with a downward opening from the interior through the bottom thereof, said hull having a circularly arrayed mounting-ledge means bordering at least a portion of said opening; a bridging structure rotatably mounted upon said ledge means and extending across said opening; an internal-combustion engine suported from and depending at least in part below said bridging structure and extending into the water beneath said hull, at least part of the combustion zone of said internalcombustion engine having wall means in contact with the water beneath the hull for cooling thereof, said engine having a generally horizontal submerged output shaft projecting from the crankcase end thereof, and a propeller mounted on said shaft, said bridging structure having an opening therethrough for passage of air from within said hull downwardly into said engine; and retaining means for securing said bridging structure down upon said mounting-ledge means, whereby the customarily bulky obstruction of the interior space within the hull that would be imposed by an inboard-mounted engine is minimized. 8. A watercraft as in claim 7, said bridging structure having a second opening therein, said second opening extending upwardly from below, said second opening constituting clearance for elevated ducting means for waste gas discharged from said engine. 9. A watercraft as in claim 8, said watercraft having also an upwardly recessed closure over said second opening, whereby the hot surface of said ducting means is guarded against contact from within said hull. 16. A watercraft as in claim 7, said bridging structure being demountable from said ledge means from within said hull, said bridging structure supporting thereupon a separately detachable fuel tank. 11. A watercraft as in claim 7, said bridging structure constituting a sealed barrier against ingress of water upwardly therethrough into the interior of said hull. 12. A watercraft in claim '7, having also a cowling enclosing said engine and confining therein a supply of cooling water therefor, said cowling being interposed between said engine and the flow of water beneath said hull and external to said cowling,

said cowling having valve means for regulating exchange of water external and internal thereof.

13. A watercraft as in claim 5,

having additional closure means, not a part of said bridging structure, extending across a portion of said opening.

14. A watercraft comprising:

a hull with a downward opening through the bottom thereof,

said hull having mounting ledge means bordering at least a portion of said opening,

said means being adapted to receive thereon from above a demountable bridging structure;

a bridging structure having a rim portion adapted to fit said ledge means,

said bridging structure being supported from below by said ledge means,

said bridging structure being in turn adapted to carry and suspend therebelow one of a class of internalcombustion engines having the following characteristics:

(a) requiring application of an external coolant upon at least part of the wall surrounding the combustion zone thereof for the purpose of removing waste heat therefrom, and

(b) having a generally horizontal output shaft that emerges under water from the crankcase end thereof and carries a propeller thereon;

a retaining array for securing and holding said bridging structure down upon said ledge means;

said bridging structure being so proportioned heightwise relative to said ledge means and the bottom of said hull that such combustion zone is projected into water below said hull,

whereby the usual height-wise and volume-wise obstruction of the interior space within said hull that would be imposed by an inboard-mounted engine is minimized.

15. A watercraft as in claim 14,

said ledge means being elevated upon a wall formation bordering at least a portion of said opening.

16. A watercraft as in claim 14,

said bridging structure having a wall portion thereupon, said wall portion forming a compartment above said engine.

17. A watercraft as in claim 14,

having also cover means positioned between said clamping array and said bridging structure.

18. A watercraft as in claim 14,

said bridging structure having a circular rim portion,

said rim portion being adapted to rotate with respect to said ledge means about a vertical axis.

19. A watercraft having a hull with a downward opening through the bottom thereof,

said hull having mounting-ledge means bordering at least a portion of the opening,

said means being adapted to receive thereupon from above a demountable propulsion-system assembly,

said assembly comprising in turn:

a bridging structure having a rim portion too large to fall through said opening and an enginemounting portion smaller than said opening,

said bridging structure being adapted for downward positioning from within said hull of said rim portion upon said ledge means;

and an internal-combustion engine of a class having characteristics as follows:

(a) requiring application of an external liquid coolant upon at least part of the wall surrounding the combustion zone thereof for removing excess heat therefrom, and

(b) having a generally horizontal output shaft that emerges from the crankcase end thereof and carries a propeller thereon,

said engine being secured to said bridging structure, said engine depending from said bridging structure below said rim portion, said bridging structure and engine being so proportioned height-wise relative to said ledge means and the bottom of said hull that at least part of the combustion-zone wall projects downwardly into the water flowing beneath said hull; and a clamping array for securing and holding said bridging structure down upon said ledge means. 20. A watercraft as in claim 19, said watercraft having also a cover sealed to said hull inboard of said engine-mounting portion of said bridging structure by gasket means, said cover being situated in way of upward passage of water from below said hull into said boat, said cover barring such water and having a sealed opening therethrough for downward passage of breathing air to said engine. 21. A watercraft as claim 20, said bridging structure being formed generally of thinwall contoured material, said bridging structure generally enclosing said engine within a compartment additionally constituted of at least one of the following:

(a) said hull, including said ledge means, and (b) said cover, said compartment thus constituted enclosing a supply of cooling water therein, said combustion-zone wall being in contact with the enclosed water. 22. A watercraft as in claim 21, said compartment having valve means therein for regulating exchange of water external and internal thereof. 23. A watercraft as in claim 21, said cover being pivotably mounted at one end thereof to said hull inboard of said gasket means beyond the respective end of said opening, said bridging structure being pivotably mounted to said hull near the opposite end of said opening, whereby said cover and said bridging structure may be raised at their respective non-pivoted ends, and said cover and said bridging structure may be rested against each other near the thus-raised ends for servicing said engine in an elevated position,

one of said cover and said bridging structure having thereon a locking member temporarily engaging the other when so resting.

24. A watercraft as in claim 1,

said ledge means constituting a generally circular track, whereby said propulsion-system assembly may be rotated thereon about a generally vertical axis for steering said watercraft.

25. A watercraft comprising:

a hull with a downward opening from the interior thereof through the bottom thereof and ledge means flanking said opening;

an upwardly projecting wall formation bordering said opening above said ledge means and supported on said hull,

said wall formation standing in way of ingress of water via said opening into said interior beyond said wall formation;

and a second ledge means positioned on said wall formation above said first-mentioned ledge means and adapted to receive thereon temporarily a demountable propulsion-system assembly,

said second ledge means comprising a retractable support,

said first-mentioned ledge means being also adapted to receive said assembly when said assembly is lowered within said wall formation by a human operator to permit said assembly to coact with water below said hull,

said propulsion-system assembly including one of a class of internal-combustion engines principally cooled by immersion of the wall of the combustion Zone thereof in water,

whereby it is unnecessary to pump and circulate the Water coolant upwardly within the said hull.

References Cited by the Examiner UNITED STATES PATENTS 1,754,983 5/1930 Cumbo 41 1,786,997 12/1930 Harvey 115-41 1,840,948 1/1932 Harvey 115-41 1,874,988 8/1932 Harvey 115-41 X 2,103,183 12/1937 Rockwell 1l534 2,343,313 3/ 1944 Maynes l1534 2,466,635 5/1949 Brown et a1 1154l X 3,170,436 2/1965 Deutsch 1l541 FERGUS S. MIDDLETON, Primary Examiner.

MILTON BUCHLER, Examiner.

R. BESHA, Assistant Examiner, 

2. A WATERCRAFT HAVING A HULL WITH A DOWNWARD OPENING THROUGH THE BOTTOM THEREOF; AN UPWARDLY PROJECTING WALL FORMATION SUPPORTED ON SAID HULL AND BORDERING SAID OPENING; A MOUNTING LEDGE MEANS SURMOUNTING AT LEAST A PORTION OF SAID WALL FORMATION AND ADAPTED TO RECEIVE THEREON A DEMOUNTABLE PROPULSION-SYSTEM ASSEMBLY, SAID WALL FORMATION BEING ADJUSTABLE AS TO HEIGHT OF RISE OF SAID LEDGE MEANS WITHIN SAID HULL, SAID WALL FORMATION BEING ATTACHED TO SAID HULL AND CONSISTING AT LEAST IN PART OF FLEXIBLE MATERIAL INTERVENING BETWEEN SAID HULL AND SAID LEDGE MEANS. 